Lipofuscin pigment accumulation in the central nervous system of the mouse during aging

Antibiotics that target mitochondria extend lifespan in C. elegans

Aging is a continuous degenerative process caused by a progressive decline of cell and tissue functions in an organism. It is induced by the accumulation of damage that affects normal cellular processes, ultimately leading to cell death. It has been speculated for many years that mitochondria play a key role in the aging process. In the aim of characterizing the implications of mitochondria in aging, here we used Caenorhabditis elegans (C. elegans) as an organismal model treated a panel of mitochondrial inhibitors and assessed for survival. In our study, we assessed survival by evaluating worm lifespan, and we assessed aging markers by evaluating the pharyngeal muscle contraction, the accumulation of lipofuscin pigment and ATP levels. Our results show that treatment of worms with either doxycycline, azithromycin (inhibitors of the small and the large mitochondrial ribosomes, respectively), or a combination of both, significantly extended median lifespan of C. elegans, enhanced their pharyngeal pumping rate, reduced their lipofuscin content and their energy consumption (ATP levels), as compared to control untreated worms, suggesting an aging-abrogating effect for these drugs. Similarly, DPI, an inhibitor of mitochondrial complex I and II, was capable of prolonging the median lifespan of treated worms. On the other hand, subjecting worms to vitamin C, a pro-oxidant, failed to extend C. elegans lifespan and upregulated its energy consumption, revealing an increase in ATP level. Therefore, our longevity study reveals that mitochondrial inhibitors (i.e., mitochondria-targeting antibiotics) could abrogate aging and extend lifespan in C. elegans.

Occurrence and characterization of lipofuscin and ceroid in human atherosclerotic plaque

Atherosclerotic plaque formation starts early in life, develops silently over decades, and often displays clear evidence of accelerated biological aging. Lipofuscin has been classically defined as "the most consistent and phylogenetically conserved cellular morphologic change of aging," however, despite this traditional view different lines of evidence have recently demonstrated that, besides aging, various noxious influences can engeder its accumulation in cells and also that specific experimental conditions can revert this effect. Lipofuscin has been also proven to interact with disease-related factors to enhance cell loss. Along with lipofuscin, ceroid, another autofluorescent lipopigment usually produced under various pathological conditions unrelated to aging, has been suggested to jeopardize cell performance and viability by inducing membrane fragility, mitochondrial dysfunction, DNA damage, and oxidative stress-induced apoptosis. With regard to atherosclerosis, very few investigations have been conducted to assess whether a link could exist between lipofuscin/ceroid accumulation and the progression of the disease and no information still exist regarding the anatomy and the ultrastructural diversification of lipofuscin and ceroid in the lesional vascular tissue. At the same time, data concerning their potential toxicity at the cellular level are fragmentary, dated, and scarce. The present study investigates the occurrence and distribution of lipofuscin and ceroid in human atherosclerotic plaque and adjacent healthy tissues and analyzes the ultrastructural changes associated with their accumulation within the cell.

Aging without Apolipoprotein D: Molecular and cellular modifications in the hippocampus and cortex

A detailed knowledge of the mechanisms underlying brain aging is fundamental to understand its functional decline and the baseline upon which brain pathologies superimpose. Endogenous protective mechanisms must contribute to the adaptability and plasticity still present in the healthy aged brain. Apolipoprotein D (ApoD) is one of the few genes with a consistent and evolutionarily conserved up-regulation in the aged brain. ApoD protecting roles upon stress or injury are well known, but a study of the effects of ApoD expression in the normal aging process is still missing. Using an ApoD-knockout mouse we analyze the effects of ApoD on factors contributing to the functional maintenance of the aged brain. We focused our cellular and molecular analyses in the cortex and hippocampus at an age representing the onset of senescence where mortality risks are below 25%, avoiding bias towards long-lived animals. Lack of ApoD causes a prematurely aged brain without altering lifespan. Age-dependent hyperkinesia and memory deficits are accompanied by differential molecular effects in the cortex and hippocampus. Transcriptome analyses reveal distinct effects of ApoD loss on the molecular age-dependent patterns of the cortex and hippocampus, with different cell-type contributions to age-regulated gene expression. Markers of glial reactivity, proteostasis, and oxidative and inflammatory damage reveal early signs of aging and enhanced brain deterioration in the ApoD-knockout brain. The lack of ApoD results in an age-enhanced significant reduction in neuronal calcium-dependent functionality markers and signs of early reduction of neuronal numbers in the cortex, thus impinging upon parameters clearly differentiating neurodegenerative conditions from healthy brain aging. Our data support the hypothesis that the physiological increased brain expression of ApoD represents a homeostatic anti-aging mechanism.

Impact of aging on heat shock protein expression in the substantia nigra and striatum of the female rat

Many heat shock proteins are chaperones that help refold or degrade misfolded proteins and battle apoptosis. Because of their capacity to protect against protein misfolding, they may help keep diseases of aging at bay. A few reports have examined heat shock proteins (eg. Hsp25, Hsp60, Hsp70, and heat shock cognate 70 or Hsc70) as a function of age in the striatum and nigra. In the present study, we examined the impact of aging on Hsp25, heme oxygenase 1 (HO1 or Hsp32), Hsp40, Hsp60, Hsc70, Hsc/Hsp70 interacting protein (Hip), 78 kDa glucose-regulated protein (GRP78), Hsp90, and ubiquitinated proteins in the nigra and striatum of the female rat by infrared immunoblotting. Female animals are not typically examined in aging studies, adding further to the novelty of our study. Striatal HO1 and Hsp40 were both higher in middle-aged females than in the oldest group. Hsp60 levels were also highest in middle age in the nigra, but were highest in the oldest animals in the striatum. Striatal levels of Hsc70 and the co-chaperone Hip were lower in the oldest group relative to the youngest animals. In contrast, Hsp25 rose with advancing age in both regions. Hsp25 was also colocalized with tyrosine hydroxylase in nigral neurons. Ubiquitinated proteins exhibited a trend to rise in the oldest animals in both regions, and K48 linkage-specific ubiquitin rose significantly from 4-6 to 16-19 months in the striatum. Our study reveals a complex array of age-related changes in heat shock proteins. Furthermore, the age-related rises in some proteins, such as Hsp25, may reflect endogenous adaptations to cellular stress.

Aging-related changes in RP3V kisspeptin neurons predate the reduced activation of GnRH neurons during the early reproductive decline in female mice

Kisspeptin neurons in the rostral periventricular area of the third ventricle (RP3V) play a key role in relaying the positive feedback effects of estradiol that activate gonadotropin-releasing hormone (GnRH) neurons and drive a surge in the GnRH/luteinizing hormone (LH) level. However, the precise role of kisspeptin neurons during female reproductive senescence remains unclear. Focusing on middle-aged intact female mice with irregular estrous cycles, we found a parallel decline in c-Fos-positive kisspeptin neurons and c-Fos-positive GnRH neurons at the time of the GnRH/LH surge. Furthermore, in kisspeptin neurons, the expression of estrogen receptor α (ERα), but not progesterone receptor (PR), decreased with age. Interestingly, some kisspeptin neurons in the RP3V, but none of the GnRH neurons in the rostral preoptic area (rPOA), had a characteristic cellular senescence in middle-aged mice and old mice. These data suggest that, among the groups of neurons involved in reproductive control, the kisspeptin neurons in the RP3V are likely among the earliest to undergo aging processes and thus participate in initiating the early reproductive decline.

N-terminal ataxin-3 causes neurological symptoms with inclusions, endoplasmic reticulum stress and ribosomal dislocation

Mutant ataxin-3 is aberrantly folded and proteolytically cleaved in spinocerebellar ataxia type 3. The C-terminal region of the protein includes a polyglutamine stretch that is expanded in spinocerebellar ataxia type 3. Here, we report on the analysis of an ataxin-3 mutant mouse that has been obtained by gene trap integration. The ataxin-3 fusion protein encompasses 259 N-terminal amino acids including the Josephin domain and an ubiquitin-interacting motif but lacks the C-terminus with the polyglutamine stretch, the valosin-containing protein binding region and part of the ubiquitin-interacting motif 2. Homozygous ataxin-3 mutant mice were viable and showed no apparent anatomical defects at birth. However, at the age of 9 months, homozygous and heterozygous mutant mice revealed significantly altered behaviour and progressing deficits of motor coordination followed by premature death at ∼12 months. At this time, prominent extranuclear protein aggregates and neuronal cell death was found in mutant mice. This was associated with disturbances of the endoplasmic reticulum-mediated unfolded protein response, consistent with the normal role of ataxin-3 in endoplasmic reticulum homeostasis. Thus, the ataxin-3 gene trap model provides evidence for a contribution of the non-polyglutamine containing ataxin-3 N-terminus, which mimics a calpain fragment that has been observed in spinocerebellar ataxia type 3. Consistent with the disease in humans, gene trap mice develop cytoplasmic inclusion bodies and implicate impaired unfolded protein response in the pathogenesis of spinocerebellar ataxia type 3.

Deletion of the triplet repeat encoding polyglutamine within the mouse Huntington's disease gene results in subtle behavioral/motor phenotypes in vivo and elevated levels of ATP with cellular senescence in vitro

Huntingtin (htt), the protein encoded by the Huntington's disease (HD) gene, contains a polymorphic stretch of glutamines (polyQ) near its N-terminus. When the polyQ stretch is expanded beyond 37Q, HD results. However, the role of the normal polyQ stretch in the function of htt is still unknown. To determine the contribution of the polyQ stretch to normal htt function, we have generated mice with a precise deletion of the short CAG triplet repeat encoding 7Q in the mouse HD gene (Hdh(DeltaQ)). Hdh(DeltaQ/DeltaQ) mice are born with normal Mendelian frequency and exhibit no gross phenotypic differences in comparison to control littermates, suggesting that the polyQ stretch is not essential for htt's functions during embryonic development. Adult mice, however, commit more errors initially in the Barnes circular maze learning and memory test and perform slightly better than wild-type controls in the accelerating rotarod test for motor coordination. To determine whether these phenotypes may reflect an altered cellular physiology in the Hdh(DeltaQ) mice, we characterized the growth and energy status of primary embryonic and adult Hdh(DeltaQ/DeltaQ) fibroblasts in culture. The Hdh(DeltaQ) fibroblasts exhibited elevated levels of ATP, but senesced prematurely in comparison with wild-type fibroblasts. Taken altogether, these results suggest that htt's polyQ stretch is required for modulating longevity in culture and support the hypothesis that the polyQ stretch may also modulate a htt function involved in regulating energy homeostasis.

Quantitative age-related changes in dorsal lateral geniculate nucleus relay neurons of the rat

An ultrastructural and quantitative study of the age-related changes occurring in the relay neurons of the dorsal lateral geniculate nucleus (dLGN) was carried out using male Wistar rats aged 3, 18, 24, and 28 months. Morphometric techniques were used to obtain data regarding cellular activity including soma, nuclear, and nucleolar size. Volume fractions for rough endoplasmic reticulum (RER), mitochondria, and lipofuscin, as well as numbers and sizes of mitochondria and dense bodies (DB) was also calculated. Among the few alterations found in the perikaryon, we can highlight the redistribution and fragmentation of RER and an increase and progressive aggregation of lipofuscin. Quantitative data show a significant decrease in the volume of the soma (-42.77%) and the nucleus (-33.66%), and in the volume fraction of the RER (-18.81%) and mitochondria (-10.16%). A significant increase in lipofuscin (+213.29%), and variations in size and number of mitochondria and dense bodies were also found. Some histophysiological considerations about the findings are discussed. The findings lead to the conclusion that a relative degree of morphological stability is exhibited by relay neurons, although the quantitative data show evident intracellular changes, especially from 24 to 28 months. These changes suggest that accompanying physiological alterations may occur, with putative effects on visual function during ageing.

Age, diet and injury affect the survival of facial motoneurons

Using the model of facial nerve avulsion, we have compared the effects of injury, age and diet on motoneuronal survival. One to four weeks after nerve avulsion, 50-75% motoneuron loss was quantified in ad libitum-fed rats aged 7 days (neonate), 6 months (adult) and 24 months (aging) at the time of injury. Evidence of apoptosis was found for neonatal rats at 3 days post-injury, but not for neonates examined 7 days or adult or aging rats examined 1 month after injury. Non-operated, ad libitum-fed rats showed no significant loss of facial motoneurons by 24 months. Surprisingly, non-operated rats whose food intake was restricted to 15 g standard rat chow per day from the age of 6 months lost 50% of their motoneurons by 24 months. Facial nerve avulsion of 24-month-old rats raised on this restricted diet did not result in any additional loss of motoneurons one month after injury. These results challenge the common view that aging results in neuronal loss and that dietary restriction is universally beneficial.

Immunohistochemical localization and quantification of glucose transporters in the mouse brain

A family of seven facilitative glucose transporters (Glut1-5, 7 and 8) mediates the cellular uptake of glucose. In the brain, Glut2, Glut5 and Glut8 are found at relatively low levels whereas Glut1, Glut3 and Glut4 were reported in abundance in several brain regions. Using immunofluorescence, this study investigated, compared and quantified the localization of the brain major glucose transporters, Glut1, Glut3 and Glut4, in the different cerebral areas of CD1 mice. Most of the staining of Glut1, Glut3 and Glut4 in the mouse brain coincides with observations made in rats. The results confirm the cortical neuropil distribution of Glut3, the prominence of this transporter in the mossy fiber field of the hippocampus and the Glut3 and Glut4 immunostaining of the hippocampal pyramidal cell layer. The present study also reports novel localizations of the transporters such as the presence of Glut3 in neuronal perikarya, Glut4-labeled neurons in the CA3 of the hippocampus and the subiculum. In the cerebellum, Glut3 shows subcellular localization to the base of the Purkinje cell bodies near the axon hillock. Furthermore, an important population of Golgi cells was found to be strongly immunostained for Glut4 in the granular cell layer of the cerebellum. The quantification results suggest that the relative abundance of Glut1 in the frontal and motor cortices coincides well with the high-energy demands of these brain regions. However, the Glut4-selective abundance in cerebral motor areas supports its suggested role in providing the energy needed for the control of the motor activity. The reported neuropil distribution of Glut3 seems to uphold its suggested role in synaptic energy provision and neurotransmitter synthesis. We conclude that the cellular and regional distributions of the glucose transporters in the rodent brain seem to be relevant to their corresponding functions.

Effects of AETT-induced neuronal ceroid lipofuscinosis on learning ability in rats

The behavioral effects of ceroid-lipofuscin accumulation, induced by intraperitoneal administration of acetyl-ethyl-tetramethyl-tetralin (AETT) in Wistar rats for 3 months, were examined in the present studies. A significant increase in neuronal ceroidlipofuscin was demonstrated neuropathologically as well as morphometrically. Although the AETT-intoxicated rats showed neither alteration of locomotor activity nor shock sensitivity, a significant impairment of learning ability, especially an acquisition trial in passive avoidance tests, was observed. Results of the present studies indicate the possibility that a diffuse lipofuscin accumulation causes a learning impairment in rats. The results also imply the possibility of a significant role of age-related lipofuscin accumulation in the dementing processes of human especially in the elderly.

The relationship between the rate of entry into S phase, concentration of DNA polymerase alpha, and cell volume in human diploid fibroblast-like monokaryon cells

We have examined the kinetic relationship between the rate of entry into the S phase in human diploid fibroblast-like (HDFL) monokaryon cells and (1) the concentration of DNA polymerase alpha activity and (2) the cell volume. In the former studies, a first-order dependence between the rate of entry into the S phase and the concentration of DNA polymerase alpha activity was observed, consistent with the enzyme, or a coregulated factor, being rate limiting for this metabolic process. Examination of the nature of the dependence of the rate of entry into the S phase upon cell volume revealed a more complex relationship. The results obtained in studies with synchronized cultures are consistent with the presence of two to three rate-limiting reactants when cell volume is the independent variable. Studies with asynchronous HDFL cell cultures revealed that the smallest cells in the G1 population, presumably the early G1 cells, enter the S phase at an increasing rate as a function of cell volume up to a certain size, beyond which the cells enter at a decreasing rate similar to that observed in the studies with the synchronized cultures. Similar studies examining the relationship between cell volume and the rate of entry into S phase in three established immortal cell lines revealed positive correlation between the rate of entry into S phase and cell volume throughout the size range of the G1 population. This latter observation suggests that the factors involved in the initiation of the S phase may be present in concentrations that are not rate limiting in immortal cell lines.

Effects of acetyl-L-carnitine on the brain lipofuscin content and emotional behavior in aged rats

The effects of long-term dosing with acetyl-L-carnitine (ALC) were examined in aged rats, and they were compared with those in young rats. ALC significantly reduced the lipofuscin deposition in the brain of aged rats. Emotional parameters such as locomotor activity and rearing behavior are lower in aged rats than in young rats, and these behaviors decreased in both age groups during the experiments. ALC diminished the decrease of these emotional behaviors, especially in rearing behavior in the aged rats. Furthermore, ALC had no effect on body weight gain. These results might reflect one of the main beneficial pharmacological mechanisms of ALC in clinical use.